Device discovery and connection establishment for ad hoc networks

ABSTRACT

A wireless device transmits beacon packets at periodically occurring time intervals across a wireless channel. When the wireless communications device has not formed a piconet with one or more remote devices, the device scans the wireless channel for a predetermined amount of time immediately following each of the periodically occurring time intervals. During this time a remote device may respond to the beacon packet.

FIELD OF THE INVENTION

The present invention relates to wireless communications. Moreparticularly, the present invention relates to techniques forestablishing ad hoc wireless networks.

BACKGROUND OF THE INVENTION

Short-range wireless proximity networks typically involve devices thathave a communications range of one hundred meters or less. To providecommunications over long distances, these proximity networks ofteninterface with other networks. For example, short-range networks mayinterface with cellular networks, wireline telecommunications networks,and the Internet.

IEEE 802.15.3 defines an ad hoc wireless short-range network (referredto as a piconet) in which a plurality of devices may communicate witheach other. One of these devices is called piconet coordinator (PNC),which coordinates timing and other operational characteristics for thenetwork. The remaining devices in the network are known as DEVs. Thetiming of piconets is based on a repeating pattern of “superframes” inwhich the network devices may be allocated communications resources.

A high rate physical layer (PHY) standard is currently being selectedfor IEEE 802.15.3a. The existing IEEE 802.15.3 media access controllayer (MAC) is supposed to be used as much as possible with the selectedPHY. Currently, there are two remaining PHY candidates. One of thesecandidates is based on frequency hopping application of orthogonalfrequency division multiplexing (OFDM). The other candidate is based onM-ary Binary offset Keying. The OFDM proposal is called Multiband OFDM(MBO). Moreover, in order to further develop the OFDM proposal outsideof the IEEE, a new alliance has been formed called the MultiBand OFDMAlliance (MBOA).

MBO utilizes OFDM modulation and frequency hopping. MBO frequencyhopping involves the transmission of each of the OFDM symbols at one ofthree frequency bands according to pre-defined code, referred to as aTime Frequency Code (TFC). Time Frequency Codes can be used to spreadinterleaved information bits across a larger frequency band.

Presently, there is an interest within the MBOA to create a MediumAccess Control (MAC) layer that would be used with the OFDM physicallayer instead of the IEEE 802.15.3 MAC layer. This would involvedeveloping a new procedure for device discovery and connection setup. Itis desirable for such a MAC to provide fast device discovery andconnection establishment, because ad-hoc networks can be very dynamicand connections may change quite rapidly.

Before piconets are formed, packets (such as beacons) are typicallytransmitted and received by devices in order to setup a network. Forinstance, in IEEE 802.15.3 networks, beacons are sent at the beginningof each superframe. After sending a beacon, the device must listen for apredetermined time period to determine whether there are requests tojoin the device's network. A response to such a request is scheduled fortransmission in the following beacons. Thus, they are sent in thefollowing superframes. Accordingly, in IEEE 802.15.3, connectionestablishment is not performed immediately, even in situations whereonly two devices are involved.

SUMMARY OF THE INVENTION

The present invention provides a method and device for forming apiconet. The method and device transmit a beacon packet across awireless channel during a first predetermined time interval. During asecond predetermined time interval immediately following the firstpredetermined time interval, the method and device scan the wirelesschannel and receive a piconet joining request packet from a remotewireless communications device. During a third predetermined timeinterval that immediately follows the second predetermined timeinterval, the method and device transmit a confirmation packet to theremote wireless communications device.

The present invention provides a further method and device thattransmits a first beacon packet across a wireless channel during a firstpredetermined time interval and scans the wireless channel for a secondpredetermined time interval that immediately follows the first timeinterval. During the second time interval, a request for additionalinformation is received from a remote wireless communications device. Inresponse to this request, the additional information is transmitted witha second beacon packet across the wireless channel.

In another aspect of the present invention, beacon packets aretransmitted at periodically occurring time intervals across a wirelesschannel by a wireless communications device. When the wirelesscommunications device has not formed a piconet with one or more remotedevices, the device scans the wireless channel for a predeterminedamount of time immediately following each of the periodically occurringtime intervals.

According to yet another aspect of the present invention, a wirelesscommunications device monitors a wireless channel for transmissionsduring a predetermined time interval. Also during this time interval,the wireless communications device receives a beacon packet from aremote wireless communications device. If the remote wirelesscommunications device is the only transmitting device during thepredetermined time interval, the wireless communications device sends aresponse packet to the remote device. Transmission of this responsepacket immediately follows receipt of the beacon packet.

The present invention advantageously provides for fast connectionestablishment and device discovery. Also the present invention providesfor efficient energy consumption in wireless devices. Further featuresand advantages will become apparent from the following description andaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference numbers generally indicate identical,functionally similar, and/or structurally similar elements. The drawingin which an element first appears is indicated by the leftmost digit(s)in the reference number. The present invention will be described withreference to the accompanying drawings, wherein:

FIG. 1 is a diagram of an exemplary operational environment;

FIG. 2 is a diagram showing an IEEE 802.15.3 superframe format;

FIG. 3 is a flowchart of an operation performed by a scanning device,according to one embodiment of the present invention;

FIG. 4 is a diagram of an exemplary packet format;

FIG. 5 is a diagram illustrating an operation of a beacon-transmittingdevice according to one embodiment of the present invention;

FIGS. 6A and 6B are diagrams illustrating interactions between a firstdevice and a second device, according to embodiments of the presentinvention;

FIG. 7 is a diagram illustrating an exemplary interaction between Device1 and Device 2, according to one embodiment of the present invention;

FIG. 8 is a block diagram of an exemplary wireless communicationsdevice; and

FIGS. 9 and 10 are flowcharts of operations performed by abeacon-transmitting device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

I. Operational Environment

Before describing the invention in detail, it is first helpful todescribe an environment in which the present invention may be employed.Accordingly, FIG. 1 is a diagram of an exemplary operationalenvironment. This environment includes multiple piconets 101, eachhaving a plurality of devices 102. For instance, FIG. 1 shows a piconet101 a, which includes a piconet coordinator (PNC) 102 e, and memberdevices (DEVs) 102 a-d. FIG. 1 also shows a piconet 101 b, whichincludes a PNC 102 h, as well as DEVs 102 f and 102 g.

In piconet 101 a, each of devices 102 a-d communicate with PNC 102 eacross a corresponding link 120. For example, DEV 102 a communicateswith PNC 102 e across a link 120 a. In addition, DEVs 120 a-d maycommunicate with each other directly. For instance, FIG. 1 shows DEVs102 c and 102 d communicating via a direct link 122 a.

In piconet 101 b, each of DEVs 102 f and 102 g may communicate with PNC102 h across a corresponding link 120. For instance, DEV 102 fcommunicates with PNC 102 h across a link 120 f, while DEV 102 gcommunicates with PNC 102 h across a link 120 g. Member devices inpiconet 101 b may also communicate with each other directly. Forexample, FIG. 1 shows DEVs 102 f and 102 g communicating across a link122 b.

Each of links 122 and 120 may employ various frequency hopping patterns.These patterns may include, for example, one or more Time FrequencyCodes (TFCs). In embodiments of the present invention, each piconet 101employs a particular frequency hopping pattern. These patterns mayeither be the same or different.

In addition, the environment of FIG. 1 shows a device 102 i and a device102 j. These devices are not members of piconets 101 a or 101 b. Rather,these devices monitor or scan piconet transmissions. For instance,device 102 i scans the transmissions of piconet 101 a and device 102 jscans the transmissions of piconet 101 b. Accordingly, these devices arereferred to herein as scanning devices.

Transmissions of piconets 101 a and 101 b are each based on a repeatingpattern called a superframe. Accordingly, FIG. 2 is a diagram showing anIEEE 802.15.3 superframe format. In particular, FIG. 2 shows a frameformat having superframes 202 a, 202 b, and 202 c. As shown in FIG. 2,superframe 202 b immediately follows superframe 202 a, and superframe202 c immediately follows superframe 202 b.

Each superframe 202 includes a beacon portion 204 and a non-beaconportion 206. Beacon portions 204 convey transmissions from a PNC (suchas PNC 102 e) and are used to set timing allocations and to communicatemanagement information for the piconet. For example, beacon portions 204may convey transmissions that direct devices in piconet 101 a (e.g.,DEVs 102 a-d) to employ certain frequency hopping patterns, such asspecific TFCs. In addition, according to the present invention, beaconportions 206 may be used to transmit information regarding services andfeatures of the transmitting PNC (e.g., information services,applications, games, topologies, rates, security features, etc.) or anydevice within the piconet. The transmission of such information inbeacon portions 204 may be in response to requests from devices, such asscanning devices.

Non-beacon portions 206 are used for devices to communicate dataaccording to, for example, frequency hopping techniques that employ OFDMand/or TFCs. For instance, non-beacon portions 206 may support datacommunications across links 120 and 122. In addition, devices (e.g.,DEVs 102 a-d) may use non-beacon portions 206 to transmit controlinformation, such as request messages to other devices (e.g., PNC 102e). To facilitate the transmission of traffic, each DEV may be assigneda particular time slot within each non-beacon portion 206. These timeslots may be allocated by the PNC.

II. Network Formation

The present invention streamlines network (e.g., piconet) formation anddevice discovery. This streamlining advantageously provides a fast andfluent user experience in device discovery and piconet establishment.

The basic idea of low power consuming, but feasibly fast devicediscovery is based on sending beacons at fixed intervals. Before beacontransmission, a device (e.g., a PNC or master) may synchronize itself tothe channel by measuring the channel usage (regarding MBOA devices). Forexample, before the transmission of each beacon, the channel usage maybe scanned and the beacon can be transmitted so that it causes minimuminterference to other active devices. After the beacon is transmitted,the device may monitor the channel to determine whether there are anydevices responding to the beacon.

To allow for successful device detection, the present invention providesfor the establishment of a maximum time-period that cannot be exceededwhen sending subsequent beacons. In embodiments, beacon-transmittingdevices send beacons at fixed time intervals. However, in furtherembodiments, beacons can be sent at non-fixed intervals. An example ofsuch a maximum time interval is approximately one second. Accordingly,other devices (referred to herein as scanning devices) know the amountof time necessary to scan the channel until all beacon-transmittingdevices are found. Actual beacon transmission times may be shifted byone or more symbols in order to cause minimum interference with otheractive devices. However, in implementations, such small deviations inthe alignment of beacon transmission times do not significantly increasethe time interval between beacons. Examples of such implementationsinclude ones that employ symbols having a short duration, such as OFDMsymbols of approximately 3400 ns duration.

FIG. 3 is a flowchart of an operation performed by a scanning device,such as device 102 i or 102 j, according to one embodiment of thepresent invention. Accordingly, this operation may be performed in theexemplary operational environment of FIG. 1. This operation includes aninitial step 302. In this step, the scanning device scans a channel forone or more beacons. This is performed to find all transmitting devices.This includes beacon-transmitting devices (e.g., PNCs or masters), aswell as any other network devices (e.g., DEVs or slaves). Inembodiments, the scanning device scans the channel for at least amaximum defined beacon interval time (e.g., one second) to find alldevices. However, scanning multiple beacon intervals may provide thescanning device with some additional tolerance against interference(e.g., possible colliding transmissions between neighboring MBOApiconets).

Accordingly, as a result of the scanning performed in step 302, thescanning device obtains information regarding any network (e.g.,piconet) associated with the beacon-transmitting device. For instance,by monitoring in step 302 for transmissions between beacons, thescanning device determines whether there are other devices transmittingin the channel (e.g., DEVs or slaves in a piconet with thebeacon-transmitting device).

In addition, as a result of the scanning performed in step 302, thescanning device receives one or more beacons that are associated with atleast one beacon-transmitting device. This is shown in FIG. 3 as a step304.

After the scanning device has received a beacon, it may perform variousactions. Thus, in a step 306, the scanning device determines one or morecourses of conduct. Based on this determination, one or more of steps308-316 may be performed.

For example, in a step 308, the scanning device may reject the beacon bynot replying. Also, in a step 310, the scanning device may use thebeacon for synchronization purposes.

Alternatively, in a step 312, the scanning device may send a replymessage to join the piconet. This request may also request certainactions, such as a role switch between the beacon transmitting deviceand the scanning device once the scanning device joins the piconet.

Additionally, the scanning device may request the beacon-transmittingdevice to send out more data regarding the beacon-transmitting deviceand supported services in the next beacon. As shown in a step 314, thismay include a request for data regarding supported features. Also, asshown in step 316, this may include a request for further informationregarding specific feature(s) and service(s) offered by thebeacon-transmitting device and/or the feature(s) and service(s) offeredby the existing piconet.

If step 314 or 316 is performed, the beacon-transmitting device sends aresponse in the next beacon. Accordingly, FIG. 3 shows a step 318following step 314. In this step, the scanning device receives a beaconcontaining data regarding supported features. Also, FIG. 3 shows a step320 following step 316. In step 320, the scanning device receivesfurther information regarding specific feature(s) and service(s) offeredby the beacon-transmitting device and/or the feature(s) and service(s)offered by the existing piconet. Thus, the present inventionadvantageously allows for time-consuming association and disassociationphases to be bypassed when a scanning device only needs informationregarding a beacon-transmitting device (or information regarding apiconet where the beacon-transmitting device operates). Normallyassociation may include creation of security membership that increasesassociation time.

As described above, a scanning device may respond to a beacon in steps312, 314, and 316. Accordingly, performance of each of these stepsincludes sending a transmission to the beacon-transmitting device. Inembodiments of the present invention, such transmissions are performedin accordance with a collision avoidance algorithm, such as CSMA/CA.

However, if the scanning device would be the first to join the network,then there is no slot allocation in the non-beacon portion of thesuperframe.

Thus, if the scanning device determines in step 302 that there are noother devices in the network, then steps 312, 314, and 316 may beperformed immediately after the beacon is received. This advantageouslyprovides for streamlined network formation.

FIG. 4 is a diagram of an exemplary packet format 400 that may be usedfor the exchange of information in embodiments of the present invention.Accordingly, this format may be used for beacons, transmissions inresponse to beacons, and other network traffic. As shown in FIG. 4,packet format 400 includes a preamble 401, a header portion 402, a dataportion 403, and a trailer portion 404.

Preamble 401 is used by receiving devices to obtain synchronization withthe packet. A certain preamble 401 may by used for beacon packets, whilea different preamble 401 may be used for other packets. This featureenables scanning devices to differentiate between beacons and othernetwork traffic.

Header portion 402 includes media access control (MAC) and physicallayer (PHY) headers. In addition, header portion 402 may include errorchecking bits, tail bits, and/or pad bits. The PHY header is used by thereceiving device to decode the packet correctly. The MAC header is usedto inform the receiving device of the data included in portion 403.

Table 1, below, provides an exemplary listing of information parametersconveyed in header portion 402. In this table, the left-hand columnlists parameters, while the right hand column indicates whether theparameter is associated with the PHY header, MAC header, or is extrainformation. TABLE 1 Parameter Description PHY/MAC/Extra Data rate PHYFrame length PHY Band extension PHY Destination ID MAC Source ID MACNetwork ID MAC ACK policy MAC Frame type (beacon, data, etc.) MAC Headererror check Extra

Data portion 403 includes information as defined by the MAC header inportion 402. Trailer portion 404 may include error checking bits, tailbits, and/or pad bits. Table 2 provides an exemplary listing ofparameters that may be conveyed in portion 403 for a beacon frame. Forinstance, one or more of these parameters may be included in portion 403in response to a scanning device request of step 314 or 316. TABLE 2Parameter Description Superframe duration Access period duration Neededparameters for response Network capabilities (mesh, power mode, etc.)Network condition (current data load, number of devices) Extended beaconparameters (for example name)

Table 3 provides an exemplary listing of parameters that may be conveyedin portion 403 for a beacon response type frame. A scanning device maytransmit such a frame, for example, in steps 312, 314, or 316. TABLE 3Parameter Description Device address Device capabilities Master/slaverequest Extended beacon request

FIG. 5 is a diagram illustrating an operation of a beacon-transmittingdevice along a time axis 502 according to one embodiment of the presentinvention. As shown in FIG. 5, the beacon-transmitting device transmitsbeacons at regularly occurring beacon transmission intervals (B) 504.Following each beacon transmission interval 504, the beacon-transmittingdevice operates in a receiving interval (Rx) 506, during which thedevice listens for any responses to the previously transmitted beacon.

In embodiments of the present invention, this operation (referred to asthe “advertisement stage”) is employed by a Beacon-transmitting device(e.g., a PNC or master) before other devices form a piconet with it.Accordingly, this feature advantageously provides for low powerconsumption. Also, since receiving intervals 506 immediately followbeacon transmission intervals 504, the first device to join the piconetbenefits from a fast connection setup. This allows for streamlinedpoint-to-point connections.

FIG. 5 shows each beacon transmission interval 504 interval being 10microseconds in duration, and each receiving interval 506 being 80microseconds in duration. However, other durations may be employed.Moreover, FIG. 5 shows a period 508 between beacon transmissionintervals 504 having a duration of 1,048,576 microseconds (approximately1 second). As with intervals 504 and 506, other durations may beemployed for period 508.

The timings of FIG. 5 are provided as examples. However, other timingsare within the scope of the present invention. With these timings, lowpower consumption is reached. For instance, an interval 504 and aninterval 506 are 90 microseconds in duration. In embodiments, powerconsumption is 150 milliwatts once every 1 second for 90 microseconds.This adds total consumed energy by 13.5 microWatts. Moreover,transmission duty cycle 0.001%. Therefore, in such embodiments, abeacon-transmitting device that is not connected to any network, but isavailable for contacting within 1 second, can send beacons with batterypower source for a substantially long amount of time while ensuring fastand fluent user experience in device discovery.

FIG. 6A is a diagram illustrating an interaction between a first device(Device 1) and a second device (Device 2) along a time axis 602according to one embodiment of the present invention. At the beginningof this interaction, Device 1 is a beacon transmitting device and Device2 is a scanning device. Accordingly, FIG. 6A shows Device 1 transmittingbeacons at beacon transmission intervals 504 a and 504 b and listeningfor responses to the previously transmitted beacon in receivingintervals 506 a and 506 b.

Accordingly, Device 2 enters a receiving period (Rx) 603. During thisperiod, it receives the beacon transmitted by Device 1 in interval 504b. Upon receipt of this beacon, Device 2 transmits an answer to thisbeacon in a transmitting interval 604. Device 1 receives this answer inreceiving interval 506 b. Referring to packet format 400, header 402indicates the MAC Source ID as Device 2, and the MAC Destination ID asDevice 1. In addition, data portion 403 includes master/slave request(also referred to as a MasterRoleReq or a role switch request). Bysending this parameter, Device 2 requests that it wishes to become themaster or PNC of the network.

In a transmit interval 606, Device 1 transmits a packet, which isreceived by Device 2 in receiving interval 608. This packet conveys aresponse to the answer previously transmitted by Device 2. Referringagain to packet format 400, header 402 indicates the MAC Source ID asDevice 1, and the MAC Destination ID as Device 2. In addition, dataportion 403 includes a parameter that confirms the role switch request(this confirmation is also referred to as roleSwitchConfirm). Also, dataportion 403 includes a parameter (referred to herein aswhenBeaconStarts) which indicates a time when the role switch commencesand when Device 2 transmits its first beacon.

Accordingly, FIG. 6A shows a beacon transmission interval 610 a, whichimmediately follows receiving interval 608. During this interval, Device2 transmits a beacon, which is received by Device 1 in a receivinginterval 612 a. Thus, at this point, Device 2 is the Master/PNC andDevice 1 is the slave/DEV. This pattern is repeated again in intervals610 b and 612 b.

FIG. 6B is a diagram illustrating a further interaction between Device 1and Device 2 along a time axis 602 according to one embodiment of thepresent invention. This interaction is similar to the interaction ofFIG. 6A. However, in this interaction, no role switch occurs.Accordingly, in FIG. 6B, Device 1 continues the transmission of beaconsat interval 504 c. This beacon is received by Device 2 in a receivinginterval 610.

FIGS. 6A and 6B provide examples of Device 2 being the first device tojoin the piconet of Device 1. As described above, these example showDevice 2 joining the piconet in a fast and efficient manner due toreceiving intervals 506, which immediately follow beacon transmittingintervals 504. Moreover, prior to Device 2 joining the piconet,intervals 504 and 506 allow Device 1 to consume a low amount of power.This advantageously allows Device 1 to operate on battery power for anextended duration.

As described above with reference to FIG. 3, in embodiments of thepresent invention, a scanning device may respond to a beacon byrequesting the beacon-transmitting device to send out more dataregarding its characteristics, it supported services, and its supportedfeatures. An example of this feature is shown in FIG. 7.

FIG. 7 is a diagram illustrating an exemplary interaction between Device1 and Device 2 along a time axis 702 according to an embodiment of thepresent invention. In this interaction, Device 1 transmits a beaconduring beacon transmitting intervals 704, which may occur approximatelyevery 1 second. Following each interval 704 is a receiving interval 706in which Device 1 scans for beacon responses.

FIG. 7 shows a receiving interval 708 in which Device 2 scans the beaconchannel, finds the beacon transmitted in interval 704 a, and sends aresponse in transmitting interval 710. This response includes a requestfor further information. Device 1 receives this response in receivinginterval 706 a. In response to this request, Device 1 sends a beaconextension during an extension interval 712, which immediately followsbeacon transmission interval 704 b. This extension includes informationregarding Device 1, which was requested by Device 2. Immediatelyfollowing extension interval 712 is receiving interval 706 b. Duringinterval 706 b, Device 1 scans for responses to the Beacon and Beaconextension transmitted in during intervals 704 b and 712.

Device 2 receives the beacon extension in a receive interval 714. Basedon the information in this extension, Device 2 may decide whether tojoin the piconet of Device 1. Accordingly, FIG. 7 shows intervals 704 c,706 c, and 716-726. During these intervals, Device 2 joins the piconetof Device 1 and engages in a role switch in the same manner as describedabove with reference to FIG. 6A.

III. Device Implementation

FIG. 8 is a diagram of a wireless communications device 800, which mayoperate according to the techniques of the present invention. Thisdevice may be used in various communications environments, such as theenvironment of FIG. 1. Also, device 800 may engage in communicationsaccording to various scenarios, such as those described above withreference to FIGS. 5, 6A, 6B, and 7. As shown in FIG. 8, device 800includes a physical layer (PHY) controller 802, a media accesscontroller (MAC) 803, an OFDM transceiver 804, a scanning module 806,and an antenna 810.

MAC controller 803 generates packets for wireless transmission. Inaddition, MAC controller 803 receives and processes packets that areoriginated from remote devices. MAC controller 803 exchanges thesepackets with PHY controller 802. In turn, PHY controller 802 exchangespackets with OFDM transceiver 804. These packets may be in the formatdescribed above with reference to FIG. 4.

FIG. 8 shows that OFDM transceiver 804 includes an inverse fast fouriertransform (IFFT) module 814, a zero padding module 816, an upconverter818, and a transmit amplifier 820. IFFT module 814 receives packets fortransmission from PHY controller 802. For each of these packets, IFFTmodule 814 generates an OFDM modulated signal. This generation involvesperforming one or more inverse fast fourier transform operations. As aresult, this OFDM modulated signal includes one or more OFDM symbols.This signal is sent to zero padding module 816, which appends one ormore “zero samples” to the beginning of each OFDM symbol to produce apadded modulated signal. Upconverter 818 receives this padded signal andemploys carrier-based techniques to place it into one or more frequencybands. These one or more frequency bands are determined according to afrequency hopping pattern, such as one or more of the TFCs. As a result,upconverter 818 produces a frequency hopping signal, which is amplifiedby transmit amplifier 820 and transmitted through antenna 810.

FIG. 8 shows that OFDM transceiver 804 further includes a downconverter822, a receive amplifier 824, and a fast fourier transform (FFT) module826. These components are employed in the reception of wireless signalsfrom remote devices. In particular, antenna 810 receives wirelesssignals from remote devices and sends them to downconverter 822. Thesewireless signals employ frequency hopping patterns, such as one or moreof the TFCs.

Upon receipt, downconverter 822 employs carrier-based techniques toconvert these signals from its one or more frequency hopping bands(e.g., TFC bands) into a predetermined lower frequency range. Thisresults in modulated signals, which are received by amplifier 824 togenerate amplified signals. FFT module 826 performs OFDM demodulation onthese signals. This demodulation involves performing a fast fouriertransform for each symbol that is conveyed in the amplified signals.

As a result of this demodulation, FFT module 826 produces one or morepackets, which are sent to PHY controller 802. These packets may conveyvarious information, such as payload data and protocol header(s). Uponreceipt, PHY controller 802 processes these packets. This may involveremoving certain PHY layer header fields, and passing the remainingportions of the packets to MAC controller 803.

As described above, device 800 includes a scanning module 806, which iscoupled to MAC controller 803 and antenna 810. Scanning module 806monitors energy received by antenna 810 over channels and time intervalsspecified by MAC controller 803. This monitoring may involve variousenergy detection and signal processing techniques. Based on thismonitoring, scanning module 806 provides information to MAC controller803 regarding the existence of transmissions over monitored channels.Based on this information (as well as on packets received from remotedevices), MAC controller 803 may generate packets for transmission.Accordingly, device 800 may operate as either a beacon transmittingdevice, or a scanning device, as described herein.

As shown in FIG. 8, device 800 further includes one or more upperprotocol layers 805. These layers may involve, for example, userapplications. Accordingly, upper layers 805 may exchange informationwith remote devices. This involves layer(s) 805 exchanging protocol dataunits with MAC controller 803. In turn, MAC controller 803 operates withPHY controller 802 and transceiver 804 to transmit and receivecorresponding wireless signals.

The devices of FIG. 8 may be implemented in hardware, software,firmware, or any combination thereof. For instance, scanning module 806,upconverter 818, transmit amplifier 820, receive amplifier 824, anddownconverter 822 may include electronics, such as amplifiers, mixers,and filters. Moreover, implementations of device 800 may include digitalsignal processor(s) (DSPs) to implement various modules, such asscanning module 806, IFFT module 814, zero padding module 816, and FFTmodule 826. Moreover, in embodiments of the present invention,processor(s), such as microprocessors, executing instructions (i.e.,software) that are stored in memory (not shown) may be used to controlthe operation of various components in device 800. For instance,components, such as PHY controller 802 and MAC controller, may beprimarily implemented through software operating on one or moreprocessors.

IV. Operation of Beacon-Transmitting Devices

FIGS. 9 and 10 are flowcharts illustrating operations of a device, suchas device 800. Examples of these operations are described above withreference to FIGS. 6A, 6B, and 7.

The operation of FIG. 9 includes a step 902 in which the devicetransmits a beacon packet across a wireless channel during a firstpredetermined time interval. Next, in a step 904, the device scans thewireless channel for a second predetermined time interval thatimmediately follows the first predetermined time interval.

In a step 906, the device receives a piconet joining request packet froma remote wireless communications device during the second predeterminedtime interval. In a step 908, the device transmits a confirmation packetto the remote wireless communications device. This step is performedduring a third predetermined time interval that immediately follows thesecond predetermined time interval.

The operation of FIG. 10 includes a step 1002 in which the devicetransmits a first beacon packet across a wireless channel during a firstpredetermined time interval. Next, in a step 1004, the device scans thewireless channel. This is performed during a second predetermined timeinterval, which immediately follows the first predetermined timeinterval.

In a step 1006, the device receives a request for additional informationfrom a remote wireless communications device. This occurs during thesecond predetermined time interval. In response to this request, thedevice transmits the additional information with a second beacon packetacross the wireless channel in a step 1008.

V. Conclusion

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not in limitation. For instance, although exampleshave been described involving IEEE 802.15.3 and/or IEEE 802.15.3acommunications, other short-range and longer-range communicationstechnologies are within the scope of the present invention. Moreover,the techniques of the present invention may be used with signaltransmission techniques other than OFDM and TFCs.

Accordingly, it will be apparent to persons skilled in the relevant artthat various changes in form and detail can be made therein withoutdeparting from the spirit and scope of the invention. Thus, the breadthand scope of the present invention should not be limited by any of theabove-described exemplary embodiments, but should be defined only inaccordance with the following claims and their equivalents.

1. A method of forming a piconet in a wireless communications device,the method comprising: (a) transmitting a beacon packet across awireless channel during a first predetermined time interval; (b)scanning the wireless channel for a second predetermined time interval,the second predetermined time interval immediately following the firstpredetermined time interval; (c) receiving a piconet joining requestpacket from a remote wireless communications device during the secondpredetermined time interval; and (d) transmitting a confirmation packetto the remote wireless communications device during a thirdpredetermined time interval, the third predetermined time intervalimmediately following the second predetermined time interval.
 2. Themethod of claim 1, wherein the piconet joining request includes arequest for a role switch.
 3. The method of claim 2, further comprisingreceiving a beacon packet from the remote wireless communicationsdevice.
 4. The method of claim 1, wherein the beacon packet, the piconetjoining request packet, and the confirmation packet each include one ormore OFDM symbols.
 5. The method of claim 1, wherein the wirelesschannel employs a frequency hopping pattern.
 6. A method in a wirelesscommunications device, comprising: (a) transmitting a first beaconpacket across a wireless channel during a first predetermined timeinterval; (b) scanning the wireless channel for a second predeterminedtime interval, the second predetermined time interval immediatelyfollowing the first predetermined time interval; (c) receiving a requestfor additional information from a remote wireless communications deviceduring the second predetermined time interval; and (d) transmitting theadditional information with a second beacon packet across the wirelesschannel.
 7. The method of claim 6, wherein the additional informationincludes available services from the wireless communications device. 8.The method of claim 6, wherein the additional information includesidentifiers of devices that are in a piconet with the wirelesscommunications device.
 9. The method of claim 6, wherein the wirelesschannel employs a frequency hopping pattern.
 10. A wirelesscommunications device, comprising: means for transmitting a beaconpacket across a wireless channel during a first predetermined timeinterval; means for scanning the wireless channel for a secondpredetermined time interval, the second predetermined time intervalimmediately following the first predetermined time interval; means forreceiving a piconet joining request packet from a remote wirelesscommunications device during the second predetermined time interval; andmeans for transmitting a confirmation packet to the remote wirelesscommunications device during a third predetermined time interval, thethird predetermined time interval immediately following the secondpredetermined time interval.
 11. A wireless communications device,comprising: means for transmitting a first beacon packet across awireless channel during a first predetermined time interval; means forscanning the wireless channel for a second predetermined time interval,the second predetermined time interval immediately following the firstpredetermined time interval; means for receiving a request foradditional information from a remote wireless communications deviceduring the second predetermined time interval; and means fortransmitting the additional information with a second beacon packetacross the wireless channel.
 12. A wireless communications device,comprising: means for monitoring a wireless channel for transmissionsduring a predetermined time interval; means for receiving a beaconpacket from a remote wireless communications device across the wirelesschannel during the predetermined time interval; and means for,immediately following receipt of the beacon packet, sending a responsepacket to the remote wireless communications device when the remotewireless communications device is the only device transmitting deviceduring the predetermined time interval.